A membrane roofing system generally includes a roof deck which is considered the structural supporting surface of a building extending between the surrounding exterior walls of the building. The roof deck may be constructed from plywood, metal decking or concrete or any other suitable material. Depending upon the construction, the roof deck may extend over the surrounding exterior walls or the roof deck may stop short of the exterior walls thereby forming a parapet wall, i.e., a low retaining wall at the edge of the roof deck. If desired, the membrane roofing system may also include an insulation barrier formed from polyisocyanarate or any other suitable material applied over the roof deck.
To make the roof deck and building weather resistant a single-ply membrane roof may be installed over the roof deck. The single-ply membrane roof refers to a water impermeable single sheet of polymeric material such as thermoplastic olefins, chlorinated polyethylene, polyvinyl chloride, chlorosulfanated polyethylene or ethylene propylene diene rubber (EPDM) having a preapplied hot melt adhesive. The membrane roof has heretofore been installed on the roof deck using a variety of different methods.
For example, the field or interior of the membrane roof may be held to the roof deck by the use of ballast and/or penetrating or non-penetrating fastener of a type well known in the art. An example of a penetrating fastener for retaining the field of a membrane roof installed to a roof deck is a plurality of small, circular, metal plates having a hole in the center and a roofing screw. In order to anchor the membrane roof, the small, circular, metal plates are spaced apart in rows on the membrane roof and the fastener is driven through the hole in each plate, the membrane roof, any insulation material and then into the roof deck. The metal plates are then covered by overlapping roof membrane. An example of a non-penetrating fastener is an adhesive that totally adheres the field of the membrane roof to the roof deck.
An important consideration for a membrane roof system is that the system withstand wind uplift forces. A high wind uplift rating may be required anywhere wind uplift characteristics are quite severe, e.g., very tall buildings. Consequently, in order to withstand wind uplift forces the membrane is typically fastened to the deck at close intervals over the entire membrane surface thereby minimizing the areas of membrane not secured to the roof deck. If the membrane sheets are secured only along the longitudinal edges, the width of the membrane sheets should be restricted to at least a dimension of only about 5-6 feet in order to ensure adequate resistance to wind uplift in the membrane between fastening locations.
In one process for laying single ply membranes on a roof deck, a first membrane is laid on a portion of the roof deck. After the membrane is laid, a roof membrane fastener such as a batten bar or a line of stress plates or the like is placed near the edge of the membrane. The batten bar or line of stress plates is positioned parallel to the edge and staggered parallel to the edge for the entire length of the edge. Each batten bar or stress plate is secured to the roof membrane by inserting mechanical fasteners through the batten bar or stress plate, and the membrane, and into or through the roof deck. Then another membrane is laid on the roof deck. A small portion of the second membrane overlaps the area where the batten bars or stress plates were laid on the first membrane. The overlapping edge area of the second membrane overlaps an area of the first membrane on both sides of the batten bars or line of stress plates. A weld is then applied between the lower first membrane and the upper second membrane on one side of the batten bars or line of stress plates and then another weld is applied between the two membranes on the other side of the batten bars or line of stress plates. This results in the fusion of the two membranes on both sides of the batten bars or line of stress plates, thus providing a secure dual-weld of the membranes. It will be appreciated that the significance of having a weld on each side of the fastener, i.e., dual-weld, is that under high wind loads, the membrane roofing system, especially the membrane and weld seam at the point of mechanical attachment are placed in a shear mode of failure. Normally, the strength values until failure of a weld seam in a shear mode are at least four times the strength values experienced in a peel mode. Accordingly, high wind uplift loads may be achieved and/or the number of fasteners utilized may be reduced and achieve the same wind uplift load otherwise achieved with a single weld seam.
A roof membrane welding apparatus for forming a weld on each side of a fastener is described in U.S. Pat. No. 4,834,828, incorporated herein by reference. The roof membrane welding apparatus includes a nozzle having two outlets of a fixed width for applying welds to the membranes on both sides of the roof membrane fastener and a single bifurcated weld wheel of a fixed width located in front of the nozzle to press the two membranes together after the welds have been applied. Although the welding apparatus described in U.S. Pat. No. 4,834,828 has been proven to perform satisfactorily, further improvements in the apparatus for attaching a membrane roof to a roof deck are desired. For example, it will be appreciated that different types of roof decks or roof conditions may require the use of different types of mechanical fasteners and/or roof membrane fasteners. Gypsum and tectum decks require auger type mechanical fasteners that are much larger in thread diameter than mechanical fasteners utilized in other deck materials. Accordingly, because the mechanical fasteners are larger, the roof membrane fastener used must also be wider. However, the known welding apparatus is not designed to accomodate different widths of roof membrane fasteners and apply a weld of substantially the same width along the side of the roof membrane fastener. Furthermore, the known welding apparatus is not designed to accomodate different widths of roof membrane fasteners and uniformly press the two overlapping roof membranes together adjacent the side of each roof membrane fastener regardless of the width of the roof membrane fastener used.
In view of the foregoing, an object of the present invention is to provide a dual-weld roof membrane welding apparatus for welding single-ply roof membranes and simultaneously forming a weld seam on each side of a roof membrane fastener. Another object of the present invention is to provide a dual-weld roof membrane welding apparatus that is adjustable to accomodate a variety of different size roof membrane fasteners to apply a heat weld simultaneously on each side of the fasteners. Another object of the present invention is to provide a dual-weld roof membrane welding apparatus that spans across the width of each roof membrane fastener and allows the apparatus to track alongside of the roof membrane fastener as the apparatus moves across the membrane thereby applying a weld uniformly spaced from the edge of the roof membrane fastener. Yet another object of the present invention is to provide a dual-weld roof membrane welding apparatus that includes the capability of applying welds to overlapping single ply roof membranes on both sides of a roof membrane fastener regardless of the width of the roof membrane fastener used. Another object of the present invention is to provide a dual-weld roof membrane welding apparatus that is capable of accomodating different widths of roof membrane fasteners and uniformly pressing the two overlapping roof membranes together adjacent the side of each roof membrane fastener regardless of the width of the roof membrane fastener used. Yet another object of the present invention is to provide a dual-weld roof membrane welding apparatus that is simple to use and economical to manufacture.
It will be appreciated that by using a welding apparatus that is capable of applying welds to overlapping single ply roof membranes on both sides of a roof membrane fastener, regardless of the width of roof membrane fastener used, the welding of the overlapping roof membranes can be done more efficiently. It will be further appreciated that by using a welding apparatus that is capable of accomodating different widths of roof membrane fasteners the apparatus is more effective in pressing the overlapping membranes together after welding thus providing for better welds which are more likely to hold the membranes together.